Câu hỏi:  

A x=\frac{2\pi}{3}+k2\pi;x=\frac{\pi}{4}+k\pi

B x=\pm \frac{2\pi}{3}+k2\pi;x=\frac{\pi}{4}+k\pi

C x=\frac{2\pi}{3}+k2\pi;x=\frac{\pi}{4}+k2\pi

D x=\pm \frac{2\pi}{3}+k2\pi;x=\frac{\pi}{4}+k2\pi